Replaces the deprecated scheduler_init with global_control. This should
future proof us, and completely avoids all the threading issues we were
seeing previously.

The TBB_PREVIEW_GLOBAL_CONTROL macro is required until TBB 2019U4, or 11
internally. So for simplicity we will make platforms using an older
version of TBB (RHEL7 and Ubuntu at writing) switch to scheduler init